(a) Field of the Invention
The present invention relates to easy-open, hermetically-sealed, packaging bags which are suitable for packaging boil-in-pouch foods or retort-in-pouch foods.
(b) Description of the Related Art
Hermetically-sealed bags are usually produced by filling a packaging bag with a content through an open end, closing the open end to make contact between two opposite sides of the inside of the packaging bag and then heat-sealing the opposite sides to each other. The thus produced hermetically-sealed packaging bags are unsatisfactory because when the sealability is increased by increasing the heat-sealing strength, the opening nature is deteriorated, requiring cutlery for opening to use the contents. Particularly, packaging bags to be subjected to heat processing, such as retort sterilization, needs such a high sealability as to stand the internal pressure increased by the heat processing, and are difficult to endow with good opening nature.
A method proposed to solve this problem is to heat-seal at relatively low heat-sealing temperature the inside of the open end of a packaging bag, with a sealing material which is composed of two strips bonded to each other with an adhesive and which can make a good seal with the inside of the packaging bag. This method provides a hermetically-sealed packaging bag, which has a high sealability and also has a good opening nature ensured by the peeling between the surfaces bonded by the adhesive. This method however, is poor in the productivity because of the complicated procedures for applying adhesives.